The present invention is concerned with a gas turbine inlet air cooling system, and more particularly, concerns a cooling medium control technology of a heat exchanger for cooling gas turbine inlet air.
In a conventional gas turbine inlet air cooling system (hereafter referred to as the system), there is a method of adjusting the flow of a chilled refrigerant by a temperature detection signal of gas turbine inlet air and a detection signal of a gas turbine generation of electricity output to control the chilled refrigerant that is supplied to the heat exchanger that cools gas turbine inlet air. Such a chilled refrigerant flow adjustment system is disclosed in Japanese patent Laid-open Publication, 9-119321. There is another system that sets a chilled refrigerant temperature by an ambient temperature, an ambient humidity and a temperature detection signal of gas turbine inlet air. Such a system that sets the temperature of the chilled refrigerant is disclosed in Japanese patent Laid-open Publication 9-195797.
Whereas a chilled refrigerant is supplied to a heat exchanger that cools a gas turbine inlet air, when the difference of the ambient temperature and the chilled refrigerant temperature is large, condensation of steam in the atmosphere generally occurs, resulting in water drainage. Because part of a chilled refrigerant is used for latent heat load, water generation becomes the heat loss in the gas turbine inlet air cooling. Moreover, output of the gas turbine decreases, and efficiency is reduced so that the pressure loss of the gas turbine inlet air that passes the heat exchanger increases. In addition, the water may drain and contact the gas turbine compressor, thus decreasing its efficiency.
On the other hand, if the heat exchanger does not change or condense steam in the atmophere to water, the minimum temperature in the outlet of the heat exchanger of the gas turbine inlet air is limited to the temperature of the chilled refrigerant that is supplied to the heat exchanger and only sensible heat is involved. It is desirable to reduce the unit price of generation of electricity where a system is operated all the round year. It is necessary, however, to set a refrigerant temperature at a temperature that takes into consideration the ambient temperature of winter to plan year round operation of the system so that the inlet air temperature depends on the chilled refrigerant temperature. Therefore, it is difficult to obtain economical operation of the system in the summer in view of the limitation of the hardware of the gas turbine with the refrigerant temperature during the winter.
The system disclosed in Japanese patent Laid-open Publication 9-195797 has a system that causes a refrigerant warmed by a heat exchanger to join the chilled refrigerant to be supplied from the chilled refrigerant supply apparatus. Such a system is an air cooling system that does not exchange excessive heat by controlling the temperature of a chilled refrigerant more than the dew point temperature of the steam of gas turbine inlet air. Thus, only sensible heat is removed.
For example, because a dew point temperature is 21.4 degrees centigrade when an ambient temperature is 30 degrees centigrade and ambient relative humidity is 60%, the refrigerant temperature becomes 21.4 degrees centigrade or more. Because the temperature difference of the gas turbine inlet air temperature and the chilled refrigerant temperature is small in the system, when it is compared with a case that the temperature of a chilled refrigerant is lower than the dew point temperature of gas turbine inlet air, the heat exchanger generally must be larger in size, and the chilled refrigerant flow increases. When a chilled refrigerant flow increases, bigger sized pumps and piping are required. In addition, when the heat exchanger becomes larger, gas turbine inlet air pressure loss increases, and the output of the gas turbine decreases.